University of Vermont

Evolution 101


What is the Theory of Natural Selection?

    All the diversity of life on earth - from the smallest ant to the largest tree - evolves by the process of natural selection.  Natural selection describes the means by which traits are passed on through populations over time, and is comprised of four tenants:
Natural Selection Diagram

Variation is the raw material upon which natural selection operates. Reproduction leads to a wide range of genetic variations upon which selection works. 


Genetic traits are inherited from parents and passed on to offspring via reproduction.

Every organism is adapted for how and where it lives, however periodic changes in resource availability allow subsets of these populations, and organisms with traits that are favorable to their survival, live and pass on their genes to the next generation.


Organisms with traits better suited for survival are able to out-produce other organisms, slowly changing the gene pool of the population over time. Evolution takes time, and while it can happen in a few generations, major changes in body shape and function may take millions of years.

Photographs courtesy of the University of California Museum of Paleontology: (

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Last modified October 06 2008 01:36 PM

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